Pitfalls in dosing vancomycin.

BACKGROUND: Vancomycin is a frequently used antibiotic for the treatment of methicillin-resistant gram-positive bacteria. Newer guidelines suggest dosing vancomycin to achieve a trough concentration between 15 and 20 mg/L. Achieving this higher concentration requires greater doses of the antibiotic. Even when using a nomogram, these higher doses often result in excessively elevated trough levels and increase the risk for vancomycin-associated acute kidney injury. We undertook this quality improvement project to better understand the reasons contributing to a toxic vancomycin trough level.

METHODS: Over a 9-month period, we examined all vancomycin trough concentrations greater than 25 mg/L to determine their cause.

RESULTS: Fifty-four elevated levels were identified in 38 patients. In 47 instances, adequate data were available for analysis. We could classify the etiology of the excessive levels into 4 groups: (1) incorrect timing of the blood collection, (2) improper dosing, (3) changing renal function and (4) abnormal pharmacokinetics/pharmacodynamics.

CONCLUSIONS: Educational programs could correct the first 3 problems. However, only more frequent therapeutic drug monitoring or use of another, less toxic, antibiotic would remedy the last one.